Deposition fabrication using inkjet technology

ABSTRACT

A method of fabricating a circuit lead, the method comprising: (a) depositing a slurry upon a substrate in a predetermined pattern, the substrate including a plurality of substantially uniformly patterned micropores operative to drain a fluid component of the slurry from the surface of the substrate, while maintaining conductive particles of the slurry on a surface of the substrate; and (b) drying the conductive particles to secure the conductive particles upon a surface of the substrate and provide a circuit lead. The invention also includes an electronic circuit comprising: (a) a substrate including a plurality of micropores that are substantially uniformly patterned; (b) a microchip; and (c) a circuit lead in electrical communication with the microchip and contacting the substrate, the circuit lead comprising conductive particles deposited upon the substrate by ejecting a slurry from an inkjet printer.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is claims priority to, and is a continuation of,U.S. patent application Ser. No. 10/973,106, filed Oct. 25, 2004, nowU.S. Pat. No. 7,055,756, the disclosure of which is hereby incorporatedby reference.

RELATED ART

1. Field of the Invention

The present invention is directed to inkjet printing, and morespecifically to inkjet printing utilizing conductive ink deposition tofabricate conductive patterns upon a filtered substrate.

2. Related Art

Radio Frequency Identification (RFID) tags have been developed andenvisioned to replace the bar code as the preeminent futureidentification tool. Present day methods of manufacturing RFID antennaeinclude costly plating and etching processes similar to currentsemiconductor device manufacturing techniques.

RFID is an automatic identification technology whereby digital dataencoded in an RFID tag or “smart label” is captured by a reader usingradio waves and, therefore, RFID does not require the tag or label to bevisually apparent in order to read its stored data. An RFID systemconsists of a tag, which is made up of a microchip with an antenna, anda reader with an antenna. The reader sends out electromagnetic waves andthe tag antenna is tuned to receive these waves and transmit stored dataon the microchip to the reader. RFID tags are either “passive” (nobattery) or “active” (self-powered by a battery), with a passive RFIDtag drawing power from an electromagnetic field created by the reader topower the microchip's circuits. The microchip then modulates the wavesand sends the waves back to the reader where the reader converts the newwaves into digital data. RFID tags can be read-only (stored data can beread but not changed), read/write (stored data can be altered orre-written), or a combination, in which some data is permanently storedwhile other memory is left accessible for later encoding and updates.

Therefore, there remains a need in the art for more widespread use ofRFID tags, as well as techniques, and devices produced from suchtechniques, that reduce the costs associated with RFID tag fabrication.In addition, there is a need in the art for increased quality controland consistency between devices and device subsets produced for RFIDapplications.

SUMMARY OF THE INVENTION

The present invention is directed to inkjet printing, and morespecifically to inkjet printing utilizing conductive ink deposition tofabricate conductive patterns upon a filtered substrate. The presentinvention includes methods, and devices manufactured using such methods,for fabricating RFID tags, and more specifically, RFID antennae. Thepresent invention makes use of conductive inks comprising a carrierfluid and suspended conductive particles that are ejected onto aprintable medium to create conductive patterns. The present inventionincorporates substrates having channels adapted to draw away the carrierfluid from the surface of the substrate to leave behind the conductiveparticles on the surface. In this manner, a droplet of conductive inkspreads over a smaller area than using conventional substrates andallows for greater precision and density in depositing the conductiveparticles. Exemplary substrates for use with the present invention maybe subjected to a vacuum or elevated temperature environment to dry theconductive particles and stabilize the positioning of the particles onthe substrate surface.

It is a first aspect of the present invention to provide a method offabricating a circuit lead, the method comprising: (a) depositing aslurry upon a substrate in a predetermined pattern, the substrateincluding a plurality of substantially uniformly patterned microporesoperative to drain a fluid component of the slurry from the surface ofthe substrate, while maintaining conductive particles of the slurry on asurface of the substrate; and (b) drying the conductive particles tosecure the conductive particles upon a surface of the substrate andprovide a circuit lead.

In a more detailed embodiment of the first aspect, the plurality ofmicropores are generally vertically oriented. In a further detailedembodiment, the slurry deposition is carried out using an inkjetprinter. In still a further detailed embodiment, the slurry depositionincludes repositioning at least one of the substrate and a nozzle of theinkjet printer to deposit the conductive particles upon the substrate inthe predetermined pattern. In a more detailed embodiment, the act ofdrying the substrate includes subjecting the substrate to an elevatedtemperature ambient. In a more detailed embodiment, the act of dryingthe substrate includes applying a vacuum to the substrate.

It is a second aspect of the present invention to provide a method offabricating a circuit lead, the method comprising: (a) depositing aslurry upon a filtration medium in a predetermined arrangement, thefiltration medium including a plurality of micropores in a substantiallyuniform arrangement operative to filter solid conductive components ofthe slurry from a fluid component of the slurry; (b) drying the solidconductive components to secure a substantial portion of the solidconductive components upon a surface of the filtration medium andprovide a circuit lead; and (c) mounting a microchip in electricalcommunication with the circuit lead.

In a more detailed embodiment of the second aspect, the plurality ofmicropores are generally vertically oriented. In a further detailedembodiment, the slurry deposition is carried out using an inkjetprinter. In still a further detailed embodiment, the slurry depositionincludes repositioning at least one of the filtration medium and anozzle of the inkjet printer to deposit the solid conductive componentsupon the filtration medium in the predetermined arrangement. In a moredetailed embodiment, the act of drying the filtration medium includessubjecting the filtration medium to an elevated temperature ambient. Ina more detailed embodiment, the act of drying the filtration mediumincludes applying a vacuum to the filtration medium.

It is a third aspect of the present invention to provide an electroniccircuit comprising: (a) a substrate including a plurality of microporesthat are substantially uniformly patterned; (b) a microchip; and (c) acircuit lead in electrical communication with the microchip andcontacting the substrate, the circuit lead comprising conductiveparticles deposited upon the substrate by ejecting a slurry from aninkjet printer.

In a more detailed embodiment of the third aspect, at least one of amedian width of the micropores and a median length of the micropores isless than at least one of a median width of the conductive particles anda median length of the conductive particles. In yet another moredetailed embodiment, a summation of a volume of each micropore of thesubstrate is greater than the volume of a carrier fluid of the slurry.In a further detailed embodiment, the micropores extend substantiallythrough an entire thickness of the substrate. In still a furtherdetailed embodiment, the substrate comprises a coating applied to a basesubstrate, where the base substrate includes at least one of paper, apolymer, a composite, and a semiconductor.

It is a fourth aspect of the present invention to provide an electroniccircuit comprising: (a) a substrate including a plurality of microporesin a substantially uniform arrangement; and (b) an circuit lead formedon the substrate for in electrical communication with a microchip, thecircuit lead comprising conductive particles deposited upon thesubstrate by ejecting a slurry from an inkjet printer.

In a more detailed embodiment of the fourth aspect, at least one of amedian width of the micropores and a median depth of the micropores isless than at least one of a median width of the conductive particles anda median length of the conductive particles. In yet another moredetailed embodiment, a summation of an available volume of themicropores of the substrate is greater than a volume of a carrier fluid,comprising the slurry, deposited on the substrate. In a further detailedembodiment, the micropores extend substantially through an entirethickness of the substrate. In still a further detailed embodiment, thesubstrate comprises a coating applied to a base substrate, where thebase substrate includes at least one of paper, a polymer, a composite,and a semiconductor.

It is a fifth aspect of the present invention to provide a method ofaccurately and precisely depositing conductive particles of a conductiveink from an inkjet printer, the method comprising: (a) orienting asubstrate with respect to an inkjet printer, the substrate including aplurality of generally aligned interstices adapted to filter aconductive ink; (b) depositing the conductive ink upon the substrate ina predetermined pattern using the inkjet printer, where the conductiveink comprises conductive particles and a carrier fluid; and (c) dryingthe conductive particles to mount the conductive particles upon asurface of the substrate and provide a conductive lead.

In a more detailed embodiment of the fifth aspect, the act of drying thesubstrate includes subjecting the substrate to an elevated temperatureambient. In yet another more detailed embodiment, the act of drying thesubstrate includes applying a vacuum to the substrate. In a furtherdetailed embodiment, the conductive ink deposited on the substrate ischemically compatible with the substrate. In still a further detailedembodiment, the conductive ink comprises a slurry of solid conductiveparticles and the carrier fluid. In a more detailed embodiment, the actof depositing the conductive ink includes depositing the conductive inkusing more than one nozzle of a printhead associated with the inkjetprinter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a first exemplary embodiment inaccordance with the present invention; and

FIG. 2 is an overhead view of an exemplary printer configuration thatmay be used to fabricate the antenna of the first exemplary embodimentas shown in FIG. 1.

DETAILED DESCRIPTION

The exemplary embodiments of the present invention are described andillustrated below to encompass methods, and devices produced inaccordance with such methods, for depositing conductive materials upon afiltered substrate. Of course, it will be apparent to those of ordinaryskill in the art that the preferred embodiments discussed below areexemplary in nature and may be reconfigured without departing from thescope and spirit of the present invention. In addition, those ofordinary skill will readily comprehend various devices that may befabricated in accordance with the methods discussed herein and,therefore, the disclosure is not limited to the exemplary embodimentsdiscussed herein, as these embodiments are for purposes of illustratingthe invention only. However, for clarity and precision, the exemplaryembodiments as discussed below may include optional steps or featuresthat one of ordinary skill will recognize as not being a requisite tofall within the scope of the present invention. As used herein,micropore refers to any orderly channel within a substrate adapted toenable a fluid to flow therein and having an opening inhibitingthroughput of particles having a mean diameter of 20-100 nanometers.

In fabricating a Radio Frequency Identification (RFID) antenna utilizingan inkjet printer, a number of considerations may be involved inachieving the desired conductivity, uniformity, and repeatability thatinclude, without limitation, the type conductive ink deposited, anypost-deposition treatment of the antenna, the software and printing modeutilized to deposit the ink, the printer and type of printhead used indepositing the ink, and the media upon which the ink is deposited. Whilethe present invention, as discussed herein, may appear to be directed tothe latter consideration, it is to be understood that the latterconsideration is simple one piece of the present invention.

During a conductive ink printing process, at least two mechanisms areinvolved in forming the conductive pattern: (1) deposition andsubsequent connection of the individual conductive particles to form aconductive path; and (2) absorption of a liquid carrier phase that mayinclude constituents such as, without limitation, water, a surfactant,and a humectant. To achieve the first mechanism most efficiently, arelatively smooth and solid substrate surface is favorable to reducegaps between conductive particles from elevational changes anddiscontinuities in the surface. To achieve the second mechanism,however, a surface having a non-uniform topography is advantageous toprovide hollows or cavities for the separation of the carrier fluid fromthe conductive particles, which hasten drying of the conductiveparticles stabilizing the relative position of the conductive particleson the substrate surface. Therefore, at first glance, it might appearthat these interests are competing and cannot be concurrentlyaccommodated. Nevertheless, the present invention is operative toaccommodate each of these interests without placing both in directcompetition with one another.

Referencing FIG. 1, a first exemplary embodiment comprises an RFID tag10 that includes a substrate 12 having a microchip 14 positionedthereon. Those of ordinary skill are familiar with the plethora oftechniques for mounting a microchip 14 to a substrate 12 and, therefore,an exhaustive explanation has been omitted for purposes of brevity. Themicrochip 14 includes at least one contact pad 16 in electricalcommunication with an inkjet deposited antenna 18 that comprises aplurality of conductive particles 20 deposited in a predeterminedpattern.

An exemplary substrate 12 in accordance with the present inventionincludes a generally smooth surface 22 with a plurality of openings 24within the surface of the substrate 12 leading to micropores 26 withinthe substrate. The substrate 12 is comprised of materials that are notespecially chemically reactive with the deposited components in contacttherewith and those of ordinary skill will understand the utility of thesubstrate 12 being reactively dormant during deposition of theconductive ink and later processing. The substrate 12 may be comprisedof aligned particles that are spaced apart to create micropores 26therebetween. Exemplary materials for use as the substrate 12 include,without limitation, ceramic particles. In this exemplary substrate 12,the micropores 26 are vertical and linearly oriented, however, it is tobe understood that angled micropores and non-linear micropores may beoperative with the present invention and these operative orientationslikewise fall within the scope of the present invention. It is to beunderstood that the uniformity of the substrate particles is ofincreasing importance to fabricate micropores 26 that are repeatable andgenerally aligned. In particular, the dimensions of the micropores 26are such that the mean particle size of the conductive particles 20deposited thereover will not completely plug the micropores.Commercially available substrates that may be used with the presentinvention include media from Pictorico (www.pictorico.com).

Referring to FIGS. 1 and 2, an inkjet printer 28 may be utilized todeposit the conductive particles 20 of the RFID antenna 18. The inkjetprinter 28 includes an ink reservoir 30 in fluid communication with aplurality of nozzles 32 of a printhead 34 and controls 36 operative toposition the nozzles 32 over particular locations of the substrate 12. Abitmap may be communicated to the printer 28 and translated by thecontrols 36 to create a printing sequence where the nozzles 32 of theprinthead 34 will be fired to eject ink onto the substrate 12. In thisexemplary embodiment, the ink comprises a slurry that includesconductive particles 20 and a carrier fluid 38 (See FIG. 1) that mayinclude a surfactant and a humectant. Those of ordinary skill arefamiliar with the various commercially available conductive inks thatmay be used in accordance with the present invention. Such inks include,without limitation, silver collide inks and are available from NipponPaint Company (www.nipponpaint.co.jp).

The printing sequence is operative to acknowledge the position of themicrochip 14 and contact pad 16 on the substrate 12. More specifically,the printing sequence will call for the deposition of the ink, includingthe conductive particles 20, onto the substrate 12 to form the antenna18 in electrical communication with the contact pad 16. Those ofordinary skill are familiar with the plethora of antenna designs andorientations available for use with RFID tags 10 that may be carried outusing an inkjet printer 28 in accordance with the present invention,each of which concurrently fall within the scope of the presentinvention.

Referencing FIGS. 1 and 2, ink is ejected from the nozzles 32 anddeposited onto the substrate 12 and the openings 24 therein allow thecarrier fluid 38 to be drawn into the micropores 26 and away from thesurface 22. This separation of carrier fluid 38 and conductive particles20 results in less carrier fluid 38 in contact with the conductiveparticles 20 above the surface 22, providing fewer avenues of movementfor the particles 20 in contact with carrier fluid 38 above thesubstrate surface 22. The concentration of conductive particles 20resulting from less carrier fluid 38 on the surface 22 of the substrate12 allows for more precise and accurate placement of the conductiveparticles 20, which may result in better connections between thedeposited conductive particles 20. This can be sharply contrasted withprior art systems where the droplet spread out over the substrate beforebeing considerably absorbed, creating a greater footprint. After the inkis deposited, the conductive particles 20 on the surface 22 of thesubstrate 12 are dried to stabilize the orientation of the particles onthe surface.

Drying of the conductive particles 20 on the substrate surface 22 may becarried out using numerous techniques. A first exemplary techniqueincludes subjecting the substrate 12 and deposited particles 20 toambient conditions and allowing the fluid components 38 of the ink tovaporize and effectively dry the conductive particles 20. A secondexemplary technique includes subjecting the substrate 12 and depositedparticles 20 to a vacuum to draw off the fluid components 38 of the inkand effectively dry the conductive particles 20. A third exemplarytechnique includes subjecting the substrate 12 and deposited particles20 to an elevated temperature environment to vaporize the fluid 38 andeffectively dry the conductive particles 20. A fourth exemplarytechnique includes subjecting the substrate 12 and deposited particles20 to a vacuum in a heated environment to vaporize the fluid 38 andeffectively dry the conductive particles 20. Those of ordinary skill arefamiliar with other techniques for drying a deposited material on asubstrate, and such techniques concurrently fall within the scope of thepresent invention.

It is also within the scope and spirit of the present invention tofabricate antennae 18 on the substrate 12 without a microchip 14 and/ora contact pad 16 being mounted to the substrate. In this manner, theantenna 18 is prefabricated and may be later mounted to the contact pad16 of the microchip 14 to comprise the RFID tag 10.

It is also within the scope of the present invention to mount thesubstrate 12 to another base substrate (not shown) comprising a polymer,a paper base, a semiconductor, or a composite, where the substrate 12may be applied to the base substrate prior to or subsequent todeposition of the conductive particles 20.

It is also within the scope of the present invention that the medianwidth of the micropores 26 and a median depth of the micropores 26 areless than at least one of a median width of the conductive particles 20and a median length of the conductive particles 20. It should also beunderstood that the thickness of the substrate 12 may be such that themicropores 26 extend from a top surface through to a bottom surface,thereby extending the entire thickness of the substrate 12. It is to beunderstood that the micropores 26 need not extend substantially theentire thickness of the substrate 12 in order to fall within the scopeof the present invention. Still further, the volume available within themicropores 26 of the substrate 12 is preferably greater than the volumeof the carrier fluid 38 deposited on the substrate 12, however,substrates having micropore 26 volumes less than the eventual volume ofcarrier fluid 38 deposited thereon do not necessarily fall outside ofthe scope of the present invention.

Following from the above description and invention summaries, it shouldbe apparent to those of ordinary skill in the art that, while themethods and apparatuses herein described constitute exemplaryembodiments of the present invention, the invention contained herein isnot limited to this precise embodiment and that changes may be made tosuch embodiments without departing from the scope of the invention asdefined by the claims. Additionally, it is to be understood that theinvention is defined by the claims and it is not intended that anylimitations or elements describing the exemplary embodiments set forthherein are to be incorporated into the interpretation of any claimelement unless such limitation or element is explicitly stated.Likewise, it is to be understood that it is not necessary to meet any orall of the identified advantages or objects of the invention disclosedherein in order to fall within the scope of any claims, since theinvention is defined by the claims and since inherent and/or unforeseenadvantages of the present invention may exist even though they may nothave been explicitly discussed herein.

1. A method of fabricating a circuit lead, the method comprising:depositing a slurry upon a substrate in a predetermined pattern, thesubstrate including a plurality of substantially uniformly patternedmicropores operative to drain a fluid component of the slurry from thesurface of the substrate, while maintaining conductive particles of theslurry on a surface of the substrate; and drying the conductiveparticles to secure the conductive particles upon a surface of thesubstrate and provide a circuit lead.
 2. The method of claim 1, whereinthe plurality of micropores are generally vertically oriented.
 3. Themethod of claim 1, wherein the slurry deposition is carried out using aninkjet printer.
 4. The method of claim 3, wherein the slurry depositionincludes repositioning at least one of the substrate and a nozzle of theinkjet printer to deposit the conductive particles upon the substrate inthe predetermined pattern.
 5. The method of claim 1, wherein the act ofdrying the substrate includes subjecting the substrate to an elevatedtemperature ambient.
 6. The method of claim 1, wherein the act of dryingthe substrate includes applying a vacuum to the substrate.
 7. A methodof fabricating a circuit lead, the method comprising: depositing aslurry upon a filtration medium in a predetermined arrangement, thefiltration medium including a plurality of micropores in a substantiallyuniform arrangement operative to filter solid conductive components ofthe slurry from a fluid component of the slurry; drying the solidconductive components to secure a substantial portion of the solidconductive components upon a surface of the filtration medium andprovide a circuit lead; and mounting a microchip in electricalcommunication with the circuit lead.
 8. The method of claim 7, whereinthe plurality of micropores are generally vertically oriented.
 9. Themethod of claim 7, wherein the slurry deposition is carried out using aninkjet printer.
 10. The method of claim 9, wherein the slurry depositionincludes repositioning at least one of the filtration medium and anozzle of the inkjet printer to deposit the solid conductive componentsupon the filtration medium in the predetermined arrangement.
 11. Themethod of claim 7, wherein the act of drying the filtration mediumincludes subjecting the filtration medium to an elevated temperatureambient.
 12. The method of claim 7, wherein the act of drying thefiltration medium includes applying a vacuum to the filtration medium.13. An electronic circuit comprising: a substrate including a pluralityof micropores that are substantially uniformly patterned; a microchip;and a circuit lead in electrical communication with the microchip andcontacting the substrate, the circuit lead comprising conductiveparticles deposited upon the substrate by ejecting a slurry from aninkjet printer.
 14. The electronic circuit of claim 13 wherein at leastone of a median width of the micropores and a median length of themicropores is less than at least one of a median width of the conductiveparticles and a median length of the conductive particles.
 15. Theelectronic circuit of claim 13, wherein a summation of a volume of eachmicropore of the substrate is greater than the volume of a carrier fluidof the slurry.
 16. The electronic circuit of claim 13, wherein themicropores extend substantially through an entire thickness of thesubstrate.
 17. The electronic circuit of claim 13, wherein the substratecomprises a coating applied to a base substrate, wherein the basesubstrate includes at least one of paper, a polymer, a composite, and asemiconductor.
 18. An electronic circuit comprising: a substrateincluding a plurality of micropores in a substantially uniformarrangement; and a circuit lead formed on the substrate for electricalcommunication with a microchip, the circuit lead comprising conductiveparticles deposited upon the substrate by ejecting a slurry from aninkjet printer.
 19. The electronic circuit of claim 18 wherein at leastone of a median width of the micropores and a median depth of themicropores is less than at least one of a median width of the conductiveparticles and a median length of the conductive particles.
 20. Theelectronic circuit of claim 18, wherein a summation of an availablevolume of the micropores of the substrate is greater than a volume of acarrier fluid, comprising the slurry, deposited on the substrate. 21.The electronic circuit of claim 18, wherein the micropores extendsubstantially through an entire thickness of the substrate.
 22. Theelectronic circuit of claim 18, wherein the substrate comprises acoating applied to a base substrate, wherein the base substrate includesat least one of paper, a polymer, a composite, and a semiconductor. 23.A method of accurately and precisely depositing conductive particles ofa conductive ink from an inkjet printer, the method comprising:orienting a substrate with respect to an inkjet printer, the substrateincluding a plurality of generally aligned interstices adapted to filtera conductive ink; depositing the conductive ink upon the substrate in apredetermine pattern using the inkjet printer, where the conductive inkcomprises conductive particles and a carrier fluid; and drying theconductive particles to mount the conductive particles upon a surface ofthe substrate and provide a conductive lead.
 24. The method of claim 23,wherein the act of drying the substrate includes subjecting thesubstrate to an elevated temperature ambient.
 25. The method of claim23, wherein the act of drying the substrate includes applying a vacuumto the substrate.
 26. The method of claim 23, wherein the conductive inkdeposited on the substrate is chemically compatible with the substrate.27. The method of claim 23, wherein the conductive ink comprises aslurry of solid conductive particles and the carrier fluid.
 28. Themethod of claim 23, wherein the act of depositing the conductive inkincludes depositing the conductive ink using more than one nozzle of aprinthead associated with the inkjet printer.